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Nest site characteristics of the Great-spotted Woodpecker in a bottomland riparian forest in the presence of invasive tree species

Ornis Hungarica (1): DOI: /orhu Nest site characteristics of the Great-spotted Woodpecker in a bottomland riparian forest in the presence of invasive tree species Gábor
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Ornis Hungarica (1): DOI: /orhu Nest site characteristics of the Great-spotted Woodpecker in a bottomland riparian forest in the presence of invasive tree species Gábor Ónodi * & Dániel Winkler Received: March 2, 2016 Accepted: April 15, 2016 Gábor Ónodi & Dániel Winkler Nest site characteristics of the Great-spotted Woodpecker in a bottomland riparian forest in the presence of invasive tree species. Ornis Hungarica 24(1): Abstract This study was carried out in Hungary, in an old unmanaged riparian poplar-willow forest during the breeding seasons of 2014 and The occurrence of two invasive tree species, the green ash and boxelder, is significant in the study area, which influences negatively the populations of native riparian tree species in Central Europe. We studied Great-spotted Woodpecker nest sites in the presence of these invasive species. Throughout the study period, eight and twelve nesting cavity trees were mapped. Trees were recorded in circular plots of 0.05 ha both for each mapped nest trees and random plots as well. Species, diameter at breast height and condition were recorded for each tree. Composition and diversity of nest site and random plots were compared. Distributions and preferences were calculated for nest tree use. Most of the recorded trees were invasive. Nest site plots had more native trees compared to random plots. Nest site showed higher diversity in terms of all three variables. Decayed and dead willow and white poplar hybrid trees were preferred for nesting. Dia meter at breast height of nest trees was between cm. Studies about cavity excavators in transformed habitats have high importance for nature conservation of riparian forests. Keywords: Picidae, breeding, alluvial forest, green ash, boxelder maple Összefoglalás A vizsgálatot ben, egy kezeletlen folyó-menti fűz-nyár ártéri erdőben végeztük. A területen két inváziós fafaj fordul elő, az amerikai kőris és a zöld juhar. A két faj Közép-Európa szerte negatívan befolyásolja az ártéri erdőkben őshonos fafajok állományait. A nagy fakopáncs költőterületét vizsgáltuk az említett inváziós fafajok jelenlétében. A vizsgálati periódusban 8, illetve 12 költőodút térképeztünk fel. A fás vegetációt 0,05 hektáros, kör alakú mintaterületeken mértük fel 20 költőhelyen, illetve 20 random mintaterületen. Rögzítettük a fák faját, mellmagassági átmérőjét, kondícióját. A költő- és random mintaterületek összetételét és diverzitását hasonlítottuk össze. Mind a költőhelyeken, mind a random mintaterületeken a legnagyobb arányban a két inváziós faj volt jelen, ám a költőterületeken gyakoribbak voltak az őshonos, és ritkábbak az inváziós fajok a random mintaterületekhez képest. A költőhelyeken az idősebb, korhadt, illetve holt fák nagyobb elegyarányban voltak jelen. A költőhelyek diverzitása mindhárom vegetációs változó esetében nagyobb volt. A vizsgált faj egyedei költőodúk készítésére a korhadó, valamint holt fűz és szürke nyárfákat részesítették előnyben. Ezek mellmagassági törzsátmérője cm-es között változott. Az odúkészítő fajokról szóló vizsgálatok az átalakult ártéri élőhelyeken nagy jelentőségűek a megfelelő természetvédelmi kezelések kidolgozásához. Kulcsszavak: Picidae, költés, ártéri erdők, amerikai kőris, zöld juhar Institute of Wildlife Management and Vertebrate Zoology, University of West Hungary, 9400 Sopron, Bajcsy-Zsilinszky utca 4. Hungary, *corresponding author 82 ORNIS HUNGARICA (1) Introduction Riparian forests maintain high natural and conservational value. These forests provide source-rich habitats for a high diversity of species. Alluvial forests also serve as green corridors for forest associated species to maintain their opportunities for dispersing. These habitats are highly threatened by river control management and inter alia invasive plant species. Numerous European rivers were regulated for economic reasons and their river beds were transformed to more straight statuses. In lowland Central Europe, riparian forests have two main distinguished types: the willow-poplar forests (softwood gallery forests), situated closer to the river bed; and further away, the oak-ash-elm forests (hardwood gallery forests). Distribution of hardwood gallery forests has drastically decreased as a result of river control, dam management or forest clearing for agricultural land use. Most softwood gallery forests of Hungary are composed of poplar and willow species with dominant native species like white poplar (Populus alba), black poplar (Populus nigra), white willow (Salix alba) and crack willow (Salix fragilis). Because of their high genetic similarity, the Hungarian distribution of aspen (Populus tremula) and white poplar overlap; thus, hybrids with high variability and introgressive populations of poplars are present in the riparian forests. Due to the extensive distribution of planted hybrid poplar (P. euramericana), nowadays the majority of trees that resemble black poplar in these forests are most likely hybrids of black poplar and the planted Euamerican poplars (Haraszthy 2001, Gencsi & Vancsura 2002). Floodplain forests are especially at risk of alien plant invasion because of the permanent propagulum supply and the presence of moist, nutrient-rich disturbed habitats which are very suitable for new establishment. Among the invasive tree species the green ash (Fraxinus pennsylvanica) and boxelder (Acer negundo) are the most notable mainly in the underand midstorey level. Due to their abundant and effective dispersed fruits, rapid growth and good regenerative capacities, they have a strong transformative effect on the species composition of floodplain forests by hindering the renewal of native species, of which very few seedlings and saplings can be found in such forests. They influence the chemical traits of the soil and also develop a second canopy layer under the canopy of native trees and thus increasingly shade the ground preventing the saplings of the autochtonous trees from growing properly (Csiszár & Bartha 2008, Udvardy 2008, Erfmeier et al. 2011). In North America, the green ash and the boxelder maple are considered to be mid-successional species as they live in an intermedier lane between the early-successional willow-poplar and the late-successional ash-elm riparian forests. Our focal species are present in the midstorey and the lower canopy layer of the two above-mentioned habitats. They tolerate the higher ground water levels and floods less and the droughts more than the willow and poplar species (Rumble & Gobeille 1998). In addition to the above-mentioned habitat preferences of the two species, the river control managements happened to be beneficial for the green ash and the boxelder maple as the floods are scarcer and the level of ground water is deeper. These species survive more successfully in the shade and grow better at the clearings of the source-rich European riparian forests, than the European willow and poplar species (Saccone et al. 2010, Porté et al. 2011). These species also produce allelopathic chemicals that can prevent the saplings of native species from developing properly (Csiszár 2009, Csiszár et al. 2013). As a result, there G. Ónodi & D. Winkler 83 are very few saplings of the native species in the study area, making these habitats more homogenous than one and a half century ago. Nowadays, aging poplar and willow trees and various generations of these two invasive species can be found simultaneously in these forests. This is a widespread environmental problem in the bottomland riparian forests of Central Europe (Mihály & Botta-Dukát 2004, Erfmeier et al. 2011). Picid birds (Picidae) can be considered as keystone species playing key role in forest ecosystems (Gorman 2011). A total of 277 species are known worldwide, while only 11 species are native to Europe (9 of them are breeding in Hungary) (Lammertink 2014). These species live in woody habitats and feed mainly on arthropods. Cavity-excavator species can only breed in habitats where trees are old and thick enough to allow for the production of cavities within them (Gorman 2004). A high number of animal species depend on tree cavities. Among others, cavity-excavators can provide nesting opportunities for other cavity-dwelling species. Cavity-nester birds include ducks (Anatidae), owls (Strigidae), doves (Columbidae), flycatchers (Muscicapidae) and tits (Paridae) etc., while the most frequent mammalian cavity-dweller species are rodents (Rodentia) and bats (Chiroptera) (Bai et al. 2005, Politi et al. 2010). Apart from vertebrates, we can also find several examples for secondary cavity-dwelling invertebrates including wasps (Hymenoptera) or butterflies (Lepidoptera).To maintain the diversity of cavity-dwellers, it is essential to protect the cavity-excavators as well. Woodpeckers can be considered as umbrella species since through their protection it is possible to protect other species. Each woodpecker species has distinct habitat preferences in terms of both foraging and nesting. Habitat utilization studies of cavity excavator species can support the conservation of their secondary cavity-dweller species as well (Ross et al. 1997, Mazgajski 1998, Martin & Eadie 1999, Adkins Giese & Cuthbert 2003, Melletti & Penteriani 2003, Kosiński & Winiecki 2004, Martin et al. 2004, Kosiński et al. 2006, Pasinelli 2007, Roberge et al. 2008a, 2008b, Vaillancourt et al. 2008, Wan et al. 2008, Hebda 2009, Kozma 2009, Edman et al. 2011, Gorman 2011, Cooke & Hannon 2012). Numerous works have examined the nest site use of certain woodpecker species (Mazgajski 1998, Kosiński & Winiecki 2004, Pasinelli 2007, Hebda 2009, Kozma 2009). Nevertheless, one can barely find any such studies that took place in habitats highly transformed by invasive plant species. There is an increasing need for such studies, as there are altered habitats worldwide with actual range expansion. According to climate change scenarios, habitat transformations will spread around the globe (Starzomski 2013). There is a huge lack of knowledge about the mentioned, altered riparian habitats, though this environmental problem is considered to be widespread in Central Europe. Beyond the changes in vegetation characteristics, the fauna and so the cavity-nesting communities happened to be affected by this problem. The Great-spotted Woodpecker (Dendrocopos major) is the most common woodpecker species in Europe, being present with high densities in most woody habitats, thus making the most cavities. As a generalist species could have a crucial role in such altered communities as the main cavity-excavating species. For further understanding, it is important to study the habitat use of this species in such transformed habitats (Ónodi & Csörgő 2013, 2014). The questions of our study were the following: Are there any compositional differences between the characteristics of nest site and random plots? What detailed characteristics do nest trees have? 84 ORNIS HUNGARICA (1) Material and methods Our study area was a year old unmanaged riparian poplar-willow forest (cc. 35 ha) (N 47 o 04 E 20 o 11 N 47 o 02 E 20 o 11 ) situated in the Central-Tisza Landscape Protection Area, which belongs to the Hortobágy National Park, in the floodplain area of the river Tisza (Figure 1). The following native tree species were recorded: white poplar, black poplar, white willow, crack willow. Among the overstorey species, there are some introduced tree species in the area: green ash, boxelder maple, white mulberry (Morus alba) and common hackberry (Celtis occidentalis). Among them, the green ash and the boxelder maple are known to be invasive plants as well. The midstorey consisted mainly of the saplings of the above mentioned invasive species. The other scrub layer species are European dewberry (Rubus caesius) and, at the edges, the North-American bastard indigobush (Amorpha fruticosa). Apart from the study species, the Great-spotted Woodpecker, three other woodpecker species are breeding in lower densities in the area: the Lesser-spotted Woodpecker (Dryobates minor), the Green and the Black Woodpecker (Picus viridis and Dryocopus martius). Bird census Great-spotted Woodpecker nest trees were mapped in the breeding seasons of 2014 and 2015, as we followed the chirping begging calls of the nestlings (Kosiński & Winiecki 2004, Kosiński et al. 2006, Pasinelli 2007). 8 and 12 cavity trees were mapped, respectively. None of the nest trees of the latter year were reused from the former year. Figure 1. Map of the study area (N47 o 04 ; E 20 o 11 N47 o 02 ; E20 o 11 ) 1. ábra A vizsgált terület térképe (N47 o 04 ; E 20 o 11 N47 o 02 ; E20 o 11 ) G. Ónodi & D. Winkler 85 Vegetation survey Characteristics of habitat were measured in m radius circular plots (0.05 ha) centred on 20 active woodpecker nest trees and on 20 points, randomly selected from 32 semi-random plots on a 100 m by 100 m grid. Tree species, DBH (diameter at breast height) and condition of each tree were recorded in every plot. Only trees with DBH greater than 3 cm were recorded, because this value is supposed to be the minimum diameter of trees that support prey species for the Great-spotted Woodpecker (Gorman 2004). Tree species were recorded according to the following categories: willow species (W.), black poplar and its hybrids (Pb.), white poplar and its hybrids (Pw.), green ash (A.), boxelder maple (M.), white mulberry (Mb.) and common hackberry (H.). In parallel with the current study, we have been gathering data on foraging microhabitat use of the studied species all year round. So that, both willow species were listed in one single category due to the very similar architecture and bark structure which makes difficult to identify the exact species when the branches are covered with snow. Vegetation parameters were recorded after earlier studies on woodpecker nest site utilization (Hogstad 1971, Pettersson 1983, Török & Csorba 1986, Morrison & With 1987, Török 1990, Aulén & Lundberg 1991, Suhonen & Kuitonen 1991, Engstrom & Sanders 1997, Osie juk 1998, Imbeau & Desrochers 2002, Pechacek 2006, Hogstad 2009, Czeszczewik 2010). Diameter at breast height was recorded in 10 cm intervals. The category for the thickest trees was 100 cm. Condition of trees was assigned in three categories: living trees (less than half of their branches are decayed), decaying trees (more than half of their branches are decayed, but still have living branches) and dead trees (the whole tree and all of the bran ches are dead). The thickness of the utilized part of tree was assigned to one of the following six categories: 10.1 cm, cm, cm, cm, cm, 50 cm . We estima ted the thickness of the branch relative to the biometric measures of the study species (length cm, wingspan cm) (Cramp 1985). We gathered data on the condition of the used substrate in three categories: Living, Decaying and Dead. Data analyses Chi-square test was used to compare the distributions in species, DBH and condition between nest site and random plots. Shannon diversity index was calculated for tree species, DBH and condition in the case of each plot. Diversity indices of nest site and random plots were compared through Hutcheson s diversity t-test (Hutcheson 1970, Poole 1974). The ratio of the number of native trees to the pooled number of native and invasive trees was calculated for each plot. Values of nest site and random plots were compared with two-sample t-test with Welch correction. According to the availability of each category of the three dimensions measured at random plots, frequency distributions and Jacobs selectivity indices were calculated to examine which type of trees were used and preferred for nesting cavity excavation. This index can result in values from 1 to +1, where negative values are referring to avoidance 86 ORNIS HUNGARICA (1) Tree species and positive values are referring to preference. For these measures, we only worked with trees of a DBH greater than 10 cm. Analyses were carried out with PAST 2.17c (Hammer et al. 2001). Tables were managed with Microsoft Office Excel 2007 software. Results Nest site (680) Random (566) Willow 17.79% 9.01% White poplar hybrid 13.09% 10.78% Black poplar hybrid 9.85% 3.89% Green ash 24.71% 29.86% Boxelder maple 28.68% 41.87% White mulberry 5.29% 3.89% Common hackberry 0.59% 0.71% Table 1. Frequency distributions of tree species in the nest site and random plots 1. táblázat Az egyes fafajok gyakoriság-eloszlásai a költőhelyen, illetve random plotokban. Fafajok fentről lefelé: fűz, fehér nyár hibridek, fekete nyár hibridek, amerikai kőris, zöld juhar, fehér eper, nyugati ostorfa The most frequent tree species were the invasive species, among them the most abundant is the boxelder maple, while native tree species were less abundant. At the random Tree diameter at breast height Nest site (680) Random (566) cm 32.35% 45.41% cm 23.82% 21.73% cm 14.26% 13.78% cm 8.97% 5.48% cm 6.91% 4.95% cm 3.97% 2.65% cm 3.38% 1.59% cm 2.06% 2.30% cm 1.47% 0.88% cm 1.32% 0.53% 100 cm 1.47% 0.71% Table 2. Frequency distributions of tree diameter at breast height in the nest site and random plots 2. táblázat Az egyes mellmagasságban mért törzsátmérő kategóriák gyakoriság-eloszlásai a költőhelyen, illetve random plotokban Tree condition Nest site (680) Random (566) Living 30.88% 39.93% Decaying 58.24% 53.71% Dead 10.88% 6.36% Table 3. Frequency distributions of tree condition in the nest site and random plots 3. táblázat Az egyes fakondíció kategóriák gyakoriság eloszlásai a költőhelyen, illetve random plotokban (kondíció kategóriák fentről lefelé: élő, korhadó, holt) plots, white poplar hybrids were the most abundant native trees, while willow trees were the most frequent in the nest site plots. White mulberry and common hackberry trees happened to be sporadic species. Nest site plots had less invasive trees and more native trees than random plots (Table 1). Chi 2 test showed significant difference between the two distributions (X 2 =53.955, df=6, P 0.0001). Both plot types had gradually less trees in the greater DBH categories, although thinner, younger trees were represented in lower proportions in the nest sites (Table 2). Chi 2 test showed significant difference between the two distributions (X 2 =29.885, df=9, P 0.0001). Decaying trees were represented the most and dead trees the least at both types of plots, although nest site plots had more decaying and dead trees and less living trees (Table 3). G. Ónodi & D. Winkler 87 Plot Nest site (680) Random (566) Mean SD Plot Nest site (680) Random (566) Mean SD Table 4. Tree species diversity (Shannon) in the nest site and random plots 4. táblázat Shannon diverzitási értékek a fafajok esetében a költőhelyen, illetve random plotokban Table 5. Shannon diversity indices in the case of tree diameter at breast height in the nest site and random plots 5. táblázat Shannon diverzitási értékek mellmagasságban mért törzsátmérő esetében a költőhelyen, illetve random plotokban Chi 2 test showed significant difference between the two distributions (X 2 =15.505, df=2, P 0.0001). Nest site plots showed higher diversity values in the case of tree species (Table 4), diameter at breast height (Table 5) and tree condition (Table 6). Diversity t-test showed significant differences between nest site and random plots in terms of Shannon diversity indices of tree species (t=5.607, df=953.43, P 0.0001) and diameter at breast height (t=4.8318, df=1116, P 0.0001). The t-test did not show significant differences for tree condition (t=1.4687, df=1223.7, P= ). According to the two-sample t-test with Welch correction, nest site plots had significantly higher values for ratio of the number of native t
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